Hydraulic pump



June 30, 1953 WESTBURY ETAL 2,643,613

HYDRAULIC PUMP Filed May 51, 1950 4 Sheets-Sheet 1 .D' 000, PM K. M a *5l l 0 1000 U 2000 3000 4000 1' 000001 ,a/muwe mm. perayflb.

field/ ely pram 112 14: pel'aqm.

June 1953 R. WESTBURY ETAL ,6

HYDRAULIC PUMP Filed May 31, 1950 4 Sheets-Sheet 2 June l953 R. WESTBURYETAL 2,643,613

' HYDRAULIC PUMP Filed May 31, 1950 4 Sheets-Sheet 3 Anasw Ill Jfine 30,1953 'R. WESTBURY ETAL HYDRAULIC PUMP 4 Sheets-She et 4 Filed May 31,1950 Patented June 30, 1953 HYDRAULIC PUMP Roy Westbury, Oldbury,Bridgnorth, and Peter Eric Bray and Edward Compton,

William Packenham,

England, assignors to Integral Limited, Staffordshire, England, acompany of Great Britain Application May 31, 1950, Serial No. 165,276 InGreat Britain June 2, 1949 8 Claims. (Cl. 103-5) In hydraulic systems inwhich a pump is arranged to supply pressure fluid to one or more jacks,it is seldom possible to arrange for the jacks to operate through theirfull range of movement at substantially constant pressure. For instance,in retracting certain types of aircraft undercarriages a very lowpressure may suifice for the early stages of retraction and the normalWorking pressure of the system may be necessary only when approachingthe fully retracted position. In other cases there may be a pronouncedpressure peak at one point in the jack movement, the operating pressureover the bulk of the travel being substantially less than this peak.

Variable delivery pumps are known having an oif-loading valve forautomatically regulating the delivery so as to maintain a constantpressure between zero and maximum delivery. When the pump is deliveringfluid to a service, however, the pressure is determined, not by thecharacteristics of the pump, but by the restriction in the outputcircuit to the load operated by the jack and this pressure, during muchof the operating cycle, will be lower than the pump working pressure.Under these circumstances the delivery remains constant at the maximumvalue and the power output of the pump, determined by its delivery andpressure, is less than the desired maximum. Since the pump shaftdrive,whether mechanical or electrical, has to be designed to providethe peak working power, it is obviously not being used efficiently underthese conditions.

The object of this invention is to provide a hydraulic pump which willgive a performance approximating to the theoretical requirement that,over a given range of pressures, the pump will operate at constant powerwhile at pressures below the lower limit of the range, the deliveryshould remain at the maximum value corresponding to the lower limit ofpressure and, at

the upper limit of the pressure range,,the delivery should fall to zeroat constant pressure. A typical example of this theoretical requirementis indicated by the curveAB in Fig. 1 of the accompanying drawings, theworking range of pressures being between 1000 and 4200 lbs./ sq. in.,and the curve AB being a rectangular hyperbola.

The present invention relates to two stage hydraulic pumps of the kindcomprising two pumping units arranged in tandem, the second stagepumping unit being a piston pump having a number of radial cylinderswhose pistons are operated on their Working stroke by a cam oreccentric, with which they are held in contact only by the liquidsupplied to them by the first stage pumping unit, and Ian off-loadingvalve, subject to the delivery pressure of the second stage, forautomatically controlling the delivery of the pump by relieving thefirst stage pressure back to the inlet side of the pump as the deliverypressure rises.

A pump of this kind has the performance indicated by the graph CDEBF inFig. 1. Over the range CD the first stage pumping unit, which ispreferably a gear pump, is effective. At the point D, the off-loadingvalve opens and the delivery falls, as shown by DE. Over the range EBthere is sufficient gear stage pressure to impart full stroke to thepistons of the piston stage, and the pump operates at substantiallyconstant delivery, the slight reduction in delivery from E to B beingdue to reduction in volumetric efiiciency. At the point B the gear stagepressure has fallen to a value such that the inlet valves to all of thepistons of the piston stage are not fully opened, and the delivery fallsrapidly to zero over the range BF due to progressive reduction in thestroke imparted to all of the pistons of the piston stage. As will beseen, the performance of this pump is far from the theoretical idealrepresented by the line AB. The variation in gear stage pressure withdelivery pressure in the case of this known pump is indicated by theline VWX in Fig. 2.

The present invention provides a hydraulic pump of the above kind inwhich, at a predetermined delivery pressure, one or more of the pistonsof the piston stage are automatically rendered completely inoperativewhile the other pistons are permitted to operate at full stroke.

Thus, in contradistinction to the known pump, in which all the pistonsare rendered inoperative together, the pistons of the pump according tothe invention are rendered inoperative in stages.

This result may be achieved by differential loading of the inlet valvesfor admitting pressure from the first stage pumping unit to thecylinders of the second stage or by closure of a port to cut offcompletely the first stage pressure from those cylinders of the secondstage which are to be rendered inoperative.

Thus, in the case where the'piston stage has seven cylinders, and threeof the inlet valves are loaded by strong springs and the other fourinlet valves are loaded with light springs, the pump will control theflow over three ranges. In the first range, the first stage pumping unitwill be effective, in the second range the piston stage will beeffective with all the pistons operating and in the third range thepiston stage will be effective with only four pistons operating, and thecapacity of the pump'will thus be reduced.

Twoalternative forms of pump according to the invention will now bedescribed in detail, by way of example, with reference to theaccompanying drawings, in whichi .Fig. 1, to which reference has alreadybeen made, shows graphs indicating the relationshipbetween the deliveryof the pump in gallons per 3 minute and the delivery pressure in lbs/sq.in., graph AB showing the theoretical ideal, graph CDEBF showing theperformance of the known pump above referred to and graph GHIJKBF theperformance of the pump according to the invention,

Fig. 2, to which reference has already been made, shows graphsillustrating the relationship between first stage pressure and thedelivery pressure of the known pump and of that according to theinvention,

Fig. 3 is a diagrammatic lay-out of the first form of pump,

Fig. 4 is a longitudinal section through a practical form of the pumpshown diagrammatically in Fig. 3,

Fig. 5 is a section on the line VV in Fig. i,

Fig. 6 is a section, the left hand side of the figure being taken on theline A-A in Fig. 4 and the right hand side on the line B--B in Fig. 4,and

Fig. '7 is a diagrammatic lay-out, similar to that of Fig. 2, of thesecond form of pump.

Like reference numerals designate like parts throughout the figures.

Referring first of all to Figs. 4-6, and to the accompanyingdiagrammatic Fig. 3, the pump comprises a drive shaft 10, having splinesH by means of which it may be driven, and carrying a gear wheel l2,meshing with a gear wheel IS on a shaft 14. The gear wheels l2, l3constitute the first, or gear, stage of thepump and are fed with liquidfrom an inlet i5 through a passage l6 (Fig. 5). The liquid is fed underpressure from the gear stage of the pump via a passage (I (Fig. 5) to anoff-loading valve 18. Initially, the liquid passes, as later described,through the offloading valve 18 to an annulus l9 and thence, I

through a passage 20 (Fig. 3) to an annular channel 2| (Figs. 4 and 6),whence it has access to the inlet valves 22 of the piston stage of theThe piston stage comprises seven radially arranged pistons 23 which aresuccessively given outward, or discharge, strokes by an eccentric 24mounted on the pump shaft l0. Normally, on the inlet stroke of eachpiston, the gear stage pressure in the annulus 2! hits the associatedinlet valve 22 against its spring 25, and allows liquid to enter apassage 28 (Figs. 4 and 6) and to pass thence into the associated pumpbarrel 2? through a passage 3'! (Fig. 6). The gear stage pressure thusserves to return the pistons on the suction stroke.

On the delivery stroke, each piston 23 discharges liquid from itsrespective barrel 2'! into the associated passage 2% and thence, throughan outlet valve 28 which opens against a spring 29, into an annularchannel 30. The channel 36 communicates, via an outlet 3], with anannular port 32 associated with the off-loading valve l8, and also withan outlet 33 (Fig. 4) from which the liquid delivered by the pump isdischarged.

Referring now to Fig. 3, the oil-loading valve l8 controls, in threesteps, the flow from the pump. The oiT-loading valve comprises a valvestem 42, rigidly secured in the pump housing 41 by a bolt 43. Slidablymounted on the valve stem 42 is a sleeve 44, which is also a close fitin the housing M, and in the sleeve id is fitted a floating piston 45,of slightly smaller diameter than the valve stem 132. A further sleeve45 is slidably mounted on the sleeve 4%, the upper end of sleeve t6 alsobeing a close fit in the housing 4|.

The valve [8 controls the following ports in the pump housing: An inletport 34 to which the output of the gear stage is applied via the passageIT, a low pressure return port 35, the annular port 32 leading to thehigh pressure output from the piston stage, and a return port 36 to thetank. The annular groove l9 communicates, by the passage 2a, with theinlet to the piston stage. Springs ll, 48, 5B and 52 initially hold theparts in the position illustrated in Fig. 3.

The operation of the valve 18 is as follows:

Step 1 In the initial position liquid from the gear stage can flowdirectly to the piston stage, from the inlet port 34, via the annulargroove 19 and passage 20, and also, via overlapping annular grooves 38,39 in the parts M3 and 42, an axial bore 40 in the part 42, holes 49 andoutlet port 32 directly to the pump outlet. As the delivery pressurerises, as shown by the line GH in Fig. 1, it acts, through a hole 60 inthe base of the bore in, on the small difierential cross-sectional area59 between the two bores of the sleeve M, and at 1000 lbs./sq.in. issufficient to overcome the loading of the spring 68. The sleeve 4 willthen slide downwards until stopped by a washer El loaded by the spring50. During the first part of this action the overlapping grooves 38, 39in the parts 34 and 42 are brought out of register and the surplus gearstage liquid is relieved to the port 35 by the sleeve 46 slidingdownwards against the spring 47. During the latter part, the spring Wexpands again, finally reducing the gear stage pressure to lbs/sqin. Thepiston stage of the pump is then eiiective as indicated by the line IJin Fig. 1.

In Fig. 2, the graph drawn in full lines indicates the relationship forthis pump between gear stage pressure and delivery pressure. The gearstage pressure is initially the same as the delivery pressure and itrises, as indicated by PQ to a value of 1000 lbs/sqin. Then the valve 3responds, as just described, to cause the gear stage pressure to fall,as indicated by QR, to 100 lbs/sqin.

Step 2 When the delivery pressure rises to 3200 lbs./sq.in., the gearstage pressure remaining at 100 lbs./sq.in., the delivery pressure acts,through the port 32, the holes at, and the bore 49, on the difierentialarea 59 of the sleeve tlil to overcome the load of spring 58, and thesleeve 44 will slide downwards until stopped by a washer 51 and thespring 52. During this action the spring l'i will expand further, thusreducing the gear stage pressure to 30 lbs./sq.in. as indicated by ST inFig. 2. The inlet valves [.2 to the pistons are spring loaded, threewith strong springs 25, and four with light springs and this action willhave the efiect of preventing the opening of the three strongly sprungvalves 22. Pumping will therefore continue at a reduced capacity asindicated by the line KB in Fi 1.

Step 3 loaded, as indicated by BF in Fig. 1. Any further movement of thesleeve 44 downwards will result in relief holes 54 being uncovered toopen communication between the ports 32, 36, thus preventing excessivepressure from developing.

As will be clear from Fig. l, the change in delivery pressure in threesteps provides a reasonably close approximation to the theoreticalrequirement shown by the line AB.

As an alternative to arranging for one group of three pistons to berendered inoperative before the other group of four pistons by reason ofdifierential loading of the inlet valves 22, the sleeve 44 may, asindicated in Fig. 7, be arranged to control two ports H9, 2l9, forconducting liquid from the gear stage of the pump to the inlet valves 22of the piston stage. The port H9 communicates via a passage I20 with theinlet,

valves 22 of three of the pistons and the port 2 I 9 communicates via apassage 22 with the inlet valves 22 of the other four pistons. When, atpoint J, Fig. l, the sleeve 44 moves downwards against the action of thespring 50 into contact with the washer the sleeve 44 closes the port II9 and so renders three of the plungers inoperative by depriving them ofgear stage pressure. Thereafter, at the higher delivery pressurerepresented by the point B, Fig. 1, the sleeve 44 will move down furtheragainst the spring 52 to close the port 259 and render the remainingfour pis-- tons inoperative.

. 6 redricegin steps, the hydraulic pressure prevailing in said conduit.

2. A two stage hydraulic pump as claimed in claim 1, comprising weaksprings loading certain of said inlet valves and stronger springsloading the rest of said inlet valves, the pressure in said conduitbeing-reduced, on yielding of said first abutment, to a value such thatthe inlet valves inlet valves, said spring-loaded member being It willbe appreciated that, if desired, the

pressure, either by appropriate differential loading of their inletvalves or by the provision of more than two ports, one communicatingwith each group of cylinders, which are successively closed by theoif-loading valve.

What we claim as our invention and desire to secure by Letters Patentis:

1. A two stage hydraulic pump, comprising a first pumping unit, a secondpumping unit including a plurality of radial cylinders, pistons in saidcylinders, inlet and outlet valves associated with each of saidcylinders, and positively driven means for reciprocating said pistons insaid cylinders to cause them to discharge liquid underpressure throughsaid outlet valves, a conduit for supplying liquid under pressure fromthe first pumping unit to the inlet valves of the second pumping unit,anoutlet for receiving the discharge from the outlet valves of thesecond pumping unit, a connection between said conduit and said outlet,and an off-loading. valve, responsive to the delivery pressure in saidoutlet, for controlling the hydraulic pressure in said conduit and alsocontrolling communication between said conduit and said connection, saidoffloading valve comprising a spring loaded member controlling a portfor initially allowing liquid to flow from said conduit into saidconnection, said member being arranged to close said'port in response toincrease in: the delivery pressure to a first predetermined value, apair of spring loaded washers constituting successive abutments for saidmember, as it moves in response to further increase in the deliverypressure, said abutment-s yielding successively at predeter mined highervalues of the delivery pressure, to permit of stepwise movement of themember, and a spring-loaded sleeve surrounding said member and serving,in response to movement thereof, to effect progressive opening of arelief port to arranged, on yielding of said first abutment, to closesaid first port and, on yielding of said second abutment, also to closesaid second port.

4. A two stage hydraulic pump, comprising'a first pumping unit, a secondpumping unit including a plurality of radial cylinders, pistons in saidcylinders, inlet and outlet valves associated with each of saidcylinders, and positively driven means for reciprocating said pistons insaid cylinders to cause them to discharge liquid under pressure throughsaid outlet valves, a conduit for supplying liquid under pressure fromthe first pumping unit to the inlet valves of the second pumping unit,an outlet for receiving the discharge from the outlet valves of thesecond pumping unit, and an off-loading valve, responsive to thedelivery pressure in saidoutlet, for controlling the hydraulic pressurein said conduit, said off-loading valve comprising a slidable memberexposed to the delivery pressure in said outlet, spring means balancingsaid slidable member against said delivery pressure and arranged toyield in stages in response to increase in the delivery pressure tocertain predetermined values, and means responsive to movement of saidslidable member for effecting a step wire reduction in the hydraulicpressure in said conduit from an initial high value first to a lowervalue sumcient to maintain all the pistons of the second pumping uniteffective and thereafter to a still lower value at which certain onlyofthe pistons of the second pumping unit are effective, the" other pistonsbeing inoperative.

5. A two stage hydraulic pump, comprising a first pumping unit, a secondpumping unit in cluding a plurality of radial cylinders, pistons in saidcylinders, inlet and outlet valves associated with each of saidcylinders, and positively driven means for reciprocating said pistons insaid cyl inders to cause them to discharge liquid under pressure throughsaid outlet valves, a conduit for supplying liquid under pressure fromthe first pumping unit to the inlet valves of the second pumping unit,an outlet for receiving the discharge from the outlet valves of thesecond pumping unit, and an off-loading valve, responsive to thedelivery pressure in said outlet, for controlling the hydraulic pressurein said conduit, said off-loading valve comprising a first slidablemember exposed to the delivery pressure in said outlet, spring meansbalancing said slidable member against said delivery pressure andarranged to yield in stages in response to increase in the deliverypressure to certain predetermined values.

conduit first to a lower value sufficient to main tain all the pistonsof the second pumping unit eifective and thereafter to a still lowervalue at which certain only of the pistons of said second pumping stageare effective, the other pistons being inoperative.

- 6. A two stage hydraulic pump, comprising a first pumping unit, asecond pumping unit including a plurality of radial cylinders, pistonsin said cylinders, inlet and outlet valves associated with each of saidcylinders, and positively driven means for reciprocating said pistons insaid cylinders to cause them to discharge liquid under pressure throughsaid outlet valves, a conduit for supplying liquid under pressure fromthe first pumping unit to the inlet valves of the second pumping unit,an outlet for receiving the dis charge from the outlet valves of thesecond pumping unit, a connection between said conduit and said outlet,and an oil-loading valve, responsive to the delivery pressure in saidoutlet, for controlling the hydraulic pressure in said conduit and alsocontrolling communication between said conduit and said connection, saidoff-loading valve comprising a slidable member exposed to the deliverypressure in said outlet, spring means balancing said slidable memberagainst said delivery pressure and arranged to yield in stages inresponse to increase in'the delivery pressure to certain predeterminedvalues, said slidable member maintaining said connection open so long asthe delivery pressure in said outlet is below a predetermined value, butbeing effective, when the delivery pressure reaches said predeterminedvalue to close said connection and means responsive to movement of saidslidable member for effecting a stepwise reduction in the hydraulicpressure in said conduit from an initial high value first to a lowervalue suflicient to maintain all the pistons of the second pumping uniteffective and thereafter to a still lower value at which certain only ofthe pistons of the second pumping unit are efiective, the other pistonsbeing inoperative.

'i. A two stage hydraulic pump, comprising a first pumping unit, asecond pumping unit including a plurality of radial cylinders, pistonsin said cylinders, inlet and outlet valves associated with each of saidcylinders, springs loading said inlet valves, one group of inlet valveshaving weaker loading springs than another group of inlet valves, andpositively driven means for reciprocating said pistons in said cylindersto cause them to discharge liquid under pressure through said outletvalves, a conduit for supplying liquid under pressure from the firstpumping unit to the inlet valves of the second pumping unit, an outletfor receiving the discharge from the outlet valves of the second pumpingunit, a connection between said'conduit and said outlet, and

an off-loading valve, responsive to the delivery pressure in saidoutlet, for controlling the hydraulic pressure in said conduit, saidoff-loading valve comprising a slidable member exposed to the deliverypressure in said outlet, spring means balancing said slidable memberagainst said delivery pressure and arranged to yield in stages inresponse to increase in the delivery pressure to certain predeterminedvalues. said slidable member maintaining said connection open so lgng as"the delivery pressure in said outlet 'is below a predetermined value,but being effective, when the delivery pressure reaches saidpredetermined value to close said connection, and means responsive tomovement of said slidable member for effecting a step-wise reduction inthe hydraulic pressure in said conduit from an initial high value firstto a lower value sufficient to maintain all the pistons of the secondpumping unit effective and thereafter to a still lower value at whichthe group of inlet valves with the stronger loading springs will remainclosed and the other group of outlet valves alone will be effective toadmit liquid to their respective cylinders.

8. A two stage hydraulic pump, comprising a first pumping unit, a secondpumping unit including a plurality of radial cylinders, pistons in saidcylinders, inlet and outlet valves associated with each of saidcylinders, and positively driven means for reciprocating said pistons insaid cylinders to cause them to discharge liquid under pressure throughsaid outlet valves, a conduit for supplying liquid under pressure fromthe first pumping unit to the second pumping unit, a first port leadingfrom said conduit to certain of said inlet valves, a second port leadingfrom said conduit to others of said inlet valves, and an oiiloadingvalve, responsive to the delivery pressure in said outlet, forcontrolling the hydraulic pressure in said conduit and also controllingthe flow of liquid from said conduit through said ports, saidelf-loading vaivc comprising a slidable member exposed to the deliverypressure in said outlet, spring means balancing said slidable memberagainst said delivery pressure and arranged to yield in stages inresponse to increase in the de livery pressure to certain predeterminedvalues, and means responsive to movement of said slidable member forefiecting a step-wise reduction in the hydraulic pressure in saidconduit, said slidable member being arranged to close said first portwhen the delivery pressure attains a predetermined value and to closesaid second port when the delivery pressure attains a second and higherpredetermined value.

ROY \VESTBURY. PETER ERIC BRAY.

EDWARD WILLIAM PACKENHAM.

- References Citedin the file of this patent UNITED STATES'PATENTSNumber Name Date 1,878,736 Vickers Sept. 20, 1932 1,909,972 L-e ValleyMay 23, 1933 1,978,480 Svenson Oct. 30, 1934 2,130,299 Ernst Sept. 13,1938 2,165,938 Noble July 11, 1939 2,295,833 Deschamps Sept. 15, 19422,432,553 Zilly Dec. 15, 1947

